A level Chemistry- term 1

Relative atomic mass

The average mass of an element divided by 1/12th of the mass of a C-12 atom

Orbital

A region within an atom holding up to 2 electrons with opposite spins

Rules of orbitals

-The 4s orbital fills before the 3d orbital
-Cu and Cr only half-fill the 4s orbital

TOF spectrometer

-Ionisation
-Acceleration (the positive ions are accelerated so that ions with the same charge have the same kinetic energy)
-Ion drift into the flight tube (the ions travel through a hole in the negatively charged plate into a tube with no electric field so the velocity remains constant- the velocity of the ions is proportional to their m/z value)
-Detection (the positive ions hit a negatively charged plate, gain an electron and become atoms again- this movement of electrons creates an electric current proportional to the abundance)

Electron impact

Th sample is vaporised and high energy electrons are fired, knocking off an electron and forming a positive ion- may cause fragmentation.

Electrospray ionisation

The sample is dissolved in a volatile solvent and injected through a fine needle to give a fine mist. The tip of the needle is attached to a high-voltage power supply and the particles are ionised by gaining a proton (a H+ ion). Used for substances with a higher molecular mass to avoid fragmentation.

Atomic radius 

The distance between the nucleus and the outermost occupied electron shell

Trends in atomic radius

The atomic radius across a period because as protons are added, the nuclear charge increases (electron shielding is similar) so the electrostatic force of attraction between the outer shell and nucleus increases

First ionisation energy

The enthalpy needed to remove one mole of electrons from one mole of gaseous atoms and form one mole of +1 ions

How does the ionisation energy of Al deviate from the trend

In Mg the outer electron is in a 3s subshell whereas in Al it is in a 3p subshell- the 3p has a higher energy so less energy is needed to remove the outer electron from Al

How does the ionisation of S deviate from the trend

In P there are three outer electrons so none are paired (one in each 3p orbital) whereas in S there is a pair of electrons in one of the orbitals- they have opposite spins so repel each other. This means less energy is needed to remove the outer electron in S.